First of all, I would think you would want to only pass the previous sum through the form. It should be passed to a ‘previous sum’ column. You shouldn’t be passing the rollup columns because you are only using them to calculate the sum from all entries prior to the form submit, and besides, it appears that you are requiring entry of a debit or credit…so there is no reason to pass any debits or credits from the rollup columns through the form.
You would still need to do some math to add or subtract the new credit or debit from the previous sum to get the new sum. It’s getting confusing because you want the final sum to be in the sheet. I would just calculate it in glide, but I’m not sure if there is a reason that you need that total in the sheet instead bof a glide computed column.
Just to be clear, a form will not perform any math. The math can only happen once the data is written to a table or a sheet.